Safety arrangement for furnaces



Oct. 30, 1962 J. P. FOURNIER 3,060,871

SAFETY ARRANGEMENT FOR FURNACES Filed. May 4, 1960 INVENTOR JEAN PAUL FOURN/ER y A 15 W 9 W AT TOR NE Y5 3,660,871 SAFETY GEMENT FOR ACES Jean Paul Fournier, Colombes, France, assignor to Chantiers de IAtlantique (Penhoet-Loire), Paris, France, a corporation of France Filed May 4, 1969, Ser. No. 26,761 Claims priority, application France May 19, 1959 7 Claims. ({1 110173) This invention relates to safety arrangements for steam boiler furnaces and the like, of the type comprising a safety venting outlet in a wall of the furnace which outlet is normally sealed by a loaded closure gate but is adapted to open under the effect of a pressure surge within the furnace to allow escape of excess gases and thus prevent damage to the furnace equipment and possible injury to nearby personnel.

Safety venting arrangements of this general type, sometimes known as expansion gates, are in wide use on steam boiler furnaces of small and moderate size. The gate is usually loaded by suitable weighting predetermined in accordance with the maximum prescribed internal pressure within the furnace, the arrangement being such that the gate will drop back into its sealing position of its own accord by the action of the loading weight after the excess pressure in the furnace has been dissipated. However, it has not been found practicable heretofore to apply such expansion gates to large-capacity furnaces due to the excessive size of the outlet area and excessive weight of the load that would be required in order satisfactorily to handle the large volumes and pressures involved in blow-outs that are apt to occur therein. These blow-outs are due especially to accidental ignition of deflagration or explosive mixtures formed in some part of the combustion chamber or smoke flue. It has accordingly been necessary in the past to provide the larger boilers with complicated protective systems that are expensive to construct and maintain and are of only limited reliability in view of the many possibilities of malfunction inherent to any complicated mechanism.

It is an object of this invention to provide improved safety venting means for the protection of furnaces against explosions, blow-outs and the like, which will be equally applicable to both small and large sized furnaces and will be simple and reliable. Another object is to provide such safety means which will permit resumption of normal furnace operation immediately after the venting means has operated to dissipate a dangerous pressure surge in the furnace. Other objects and advantages will appear.

Generally speaking, the invention relates to a method of protecting steam boiler furnaces against explosion blow outs and the like which consists in providing at least one wall of the furnace with a screen of free flowing granular material, the thickness of the screen being a function of the characteristics of the steam boiler.

In accordance with the invention there is provided an improved safety venting arrangement for furnaces, which comprises an opening in a wall of the furnace chamber, a pair of perforate supporting elements extending across said opening in mutually spaced relationship and a body of granular heat-resistant material contained in the space between said perforate elements and providing a continuous screen across said opening in normal conditions. Preferably means are provided for supporting an additional amount of granular material above said opening and in continuity with the body of material providing said screen whereby the latter is automatically replenished after the venting arrangement has operated.

The screen of granular, heat-resistant material (which may be sand, metal shot, or the like) may if desired be lined at the outer side thereof with a relatively thin,

i 3,050,871 Patented Oct. 30, 1962 breakable sheet of metal or the like which will provide a more positive seal against the egress of gases during normal furnace operation but will burst in case of excessive internal pressure in the furnace. In this case the depth of the screen of granular material used can be accordingly thinner. Advantageously this breakable metal sheet is mounted on a readily removable frame so as to be quickly replaceable after a blow-out and the arrangement would be such that the furnace could quite safely be operated for a reasonably short time without the additional safeguard of said metallic sheet.

The opening in the furnace wall provided with the improved sealing means of the invention may connect at its outer side with a suitable flue or conduit for discharging the vented gases to atmosphere or other disposal.

The above and further features of the invention will appear as the disclosure proceeds with reference to the accompanying drawings.

:FlG. 1 is a vertical sectional View of a safety venting device according to the invention, with related parts of the furnace structure being shown fragmentarily;

FIG. 2 is a section on line =IIII of FIG. 1;

FIG. 3 is a simplified perspective view of a boiler equipped with the venting arrangement of the invention on its front wall; and

FIG. 4 illustrates a detail modification of the device.

Referring to the drawings, there is shown at 2 the upper part of a side wall of a furnace combustion chamber 3. Formed in the wall is an opening 1. The furnace includes a set of radiant heat-screening tubes 4 and 5, extending parallel to the wall 2 and which may be spaced varying distances apart from one another. As shown, the two sets of tubes 4 and 5 are normally offset from one another and from the wall as will be especially apparent from FIG. 2, in order to provide a sufficiently large free passage area between the tubes for the egress of gases in the operation of the venting arrangement. Extending along the inner and outer sides of the opening 1 are a pair of spaced, vertically-extending perforate elements 6 and 7 respectively, each comprised of a set of horizontal, vertically-spaced slats 6' and 7', which slats are inclined inwardly and downwardly in a mutually registering relation as will be clearly seen from FIG. 1. The space defined between the two opposed sets of slats communicates at its top with the bottom outlet of a hopper or reservoir 8 above the opening 1, outside of the furnace wall 2, and which is filled with a store of heat-resistant, granular elements such as'silica for example. The mass of sand issuing from the hopper fills the vertical space between the elements 6 and 7 and so provides the screen 10. Owing to the arrangement of opposed inwardly and downwardly inclined slats the sand will be supported in a stable manner between the two support elements 6 and '7 even though the latter are fully perforate and will thus provide for free discharge of gases under excessive pressure from inside the furnace. This stable support of the mass of sand is achieved because on each opposed pair of slats 6 and 7' the sand or other granular material will form a heap sloping at the natural slope angle of the material, with the two opposed slats of each pair supporting only the weight of the related heap, while the weight of the continuous central vertical body of sand through the midplane of the opening between the support elements 6 and 7 will be transferred directly down to the wall 2 at the bottom of the opening 1.

Around the periphery of the outwardly positioned perforate supporting element 7, is mounted a fixed frame 11, and mounted in this fixed frame for quick withdrawal therefrom and insertion therein is a replaceable frame 13 which supports across it a flat metal sheet element 12 'while its lower end tapers down toward a bottom connection 16 for the discharge of sand. Deflector baffies such as 15 may be provided for guiding the escaping gases towards the outlet of the conduit as indicated by the arrows in FIG. 1.

In operation, a pressure surge due to abnormally high pressuresdeveloped in the combustion chamber 3 will sweep through the screen of sand 10, break through the frangible metal seal 12 and escape through the conduit 14 to atmosphere or other disposal. Immediately after dissipation of the pressure surge the protective sand screen 12 will reform of itsown accord by the force of gravity allowing a complement of sand to drop from hopper 8 into the space between the perforate supporting elements 6 and 7. The furnace will thus resume its normal operation substantially without interruption, and a frame 13'carrying a newmetal sealing sheet 12 may be inserted to replace the broken one, at leisure and without any hazard to the maintenance crew.

In the modification shown in FIG. 4, the inner perforate supporting element 6'consists, over at least part of the vertical extent of the opening 1, of furnace tubes 17 provided with small inclined fins 18serving a similar function to the slats 6' in the first embodiment, which latter are also shown present in the upper portion of the opening in FIG. 4.

It has been found that the improved protective arrangement for furnaces can be used with highly satisfactory results in both small and large capacity steam boilers. While the dimensions, including surface area of the opening and thickness dimension of the screen of sand or other granular material may vary greatly on individual requirements, it may be indicated that the free surface area of the opening may suitably lie within the range from /sto of the furnace section area in the case of boiler combustion chambers using substantially balanced draft, and from A: to thereof'for combustion chambers using limited pressure draft, The above figures are, of course, merelyexemplary. The depth of the granular screen should be predetermined so that the resistance opposed by said screen, plus the resistance opposed by the frangible seal if provided, shall not exceed a prescribed surge pressure.

What I claim is:

1. In a furnace combustion chamber, an exterior wall of the chamber having an opening therein, a pair of spaced perforate elementsacross said opening, a body of free-flowing heat-resistant, noncombustible granular material supported between said elements to'form a continuous screen across said opening which is permeable under pressure, means for continuously replacing said body of granular material, a relatively thin sheet of frangible material extending across the outer one of said perforate elements, to form a supplementary seal across said opening and means for discharging excess gases issuing out of said combustion chamber at a pressure sufiicient to permeate said screen of granular material and to break through said frangible sheet.

2. The combination claimed in claim 1, wherein said sheet is metallic. V

3. The combination claimed in claim 1, which includes easily-replaceable supporting means for said sheet.

4. In a furnace combustion chamber having vertical exterior walls, one of said vertical exterior walls of said chamber having an opening therein, a pair of horizontally spaced perforate supporting. assemblies extending across said opening, each assembly comprising a plurality of means defining a set of vertically-spaced, oppositely inclined surfaces, with the corresponding surfaces of the respective sets being inclined downwardly towards each other and spaced a predetermined distance from each other, hopper means overlying said opening and having a lower outlet communicating with the space between said assemblies, and a body of freefiowing heat-resistant, non-combustible granular material within said hopper means and filling said space and sup ported on said surfaces thereby to form a continuous screen across said opening serving as a pressure vent for said combustion chamber.

5 The combination claimed in claim 4, further including a frangible metal sheet extending across the outer one of said perforate assemblies to form a supplementary seal across said opening and means of discharging excess gases issuing out of said combustion chamber and through said pressure vent.

6. The combination claimed in claim 4, wherein said inclined surface defining means comprise generally horizontally extending, inclined slats.

7. The combination claimed in claim 4, which comprises boiler tubes extending horizontally in spaced relation across at least a part of the area of said opening in said combustion chamber, and wherein the inner set of said surface-defining means includes inclined fins projecting from said tubes.

References Cited in the file of this patent v UNITED STATES PATENTS 169,895 Daish Nov. 16, 1875 483,863 Platts Oct. 4, 1892 2,232,290 Szikla et al. Feb. 18, 1941 FOREIGN PATENTS 7 774,722. France 'Sept. 24, '1934 683,040 Germany V Oct. 27, 1932 

